Tubular Structure and a Method of Manufacturing Thereof

ABSTRACT

Methods and structures are disclosed. An example method includes: rotating a tubular mandrel about a longitudinal axis of the tubular mandrel; depositing a composite material on an inner surface of the tubular mandrel to form a composite tubular member on the inner surface of the tubular mandrel; inserting and expanding an inner expandable mandrel within the composite tubular member to cause the inner expandable mandrel to press the composite tubular member against the inner surface of the tubular mandrel; curing the composite tubular member; removing the inner expandable mandrel; placing a frame within the composite tubular member; and removing the tubular mandrel so as to obtain the composite tubular member with the frame placed therein.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 15/226,427, filed on Aug. 2, 2016, and entitled “Tubular Structureand a Method of Manufacturing Thereof,” the entire contents of which areherein incorporated by reference as if fully set forth in thisdescription.

FIELD

The present disclosure relates generally to a tubular structure and amethod of manufacturing thereof.

BACKGROUND

Tubular structures have a wide variety of practical uses. Tubularstructures are constructed by various methods and from variousmaterials. Designers of such tubular structures satisfy certain designcriteria (such as strength, stiffness, weight and torsional behavior) byvarying material types (fibers/resins), orientations of fiber directionsand geometric proportions of the tube itself. Another way designers havesought to improve high performance tubes is by developing newmanufacturing techniques that can reduce cost and time of manufacturingsuch tubular structures.

Existing tubular structure may be fabricated by placing a tubular memberhorizontally. Prior to insertion of a frame within the tubular member tosupport it, the tubular member might not possess enough internalstrength to support its weight. This can occur when the diameter of thetubular member is large relative to a thickness of the tubular member,e.g., when the tubular member is a fuselage of a commercial jet.Sagging, slumping, or changing the shape of the tubular member may thusoccur as a result of the horizontal positioning. To alleviate thisproblem, additional bracing, jigs, and fixtures may be used to retainthe shape of the tubular structure.

Further, the frame might not be fabricated until the tubular member iscompleted. In other words, the frame is fabricated in series with thetubular member. This may increase manufacturing time of the fuselage orany other tubular structure.

Therefore methods, processes, and structures are desired that allow forthe frame to be fabricated in parallel with the tubular member to reduceoverall manufacturing time and allow the tubular member to gain itsstructural integrity early in the fabrication process to reduce the useof bracing, jigs, and fixtures.

SUMMARY

The present disclosure describes embodiments that relate to a tubularstructure and a method of manufacturing thereof. In one aspect, thepresent disclosure describes a method. The method comprises: (i)rotating a tubular mandrel about a longitudinal axis of the tubularmandrel, wherein the tubular mandrel is vertically-oriented; (ii)depositing a composite material on an inner surface of the tubularmandrel as the tubular mandrel is rotated so as to form a compositetubular member on the inner surface of the tubular mandrel; (iii)inserting an inner expandable mandrel within the composite tubularmember; (iv) expanding the inner expandable mandrel so as to cause theinner expandable mandrel to press the composite tubular member againstthe inner surface of the tubular mandrel; (v) curing the compositetubular member while being sandwiched between the inner expandablemandrel and the tubular mandrel; (vi) removing the inner expandablemandrel; (vii) placing a frame within the composite tubular member; and(viii) removing the tubular mandrel so as to obtain the compositetubular member with the frame placed therein.

In another aspect, the present disclosure describes a tubular structure.The tubular structure comprises: (i) a composite tubular member; and(ii) a geodesic frame disposed within and contacting the compositetubular member, wherein the geodesic frame comprises twooppositely-wound spirals joined at intersection points of the twooppositely-wound spirals.

In still another aspect, the present disclosure describes a tubularstructure prepared by a process comprising: (i) rotating a tubularmandrel about a longitudinal axis of the tubular mandrel, wherein thetubular mandrel is vertically-oriented; (ii) depositing a compositematerial on an inner surface of the tubular mandrel as the tubularmandrel is rotated so as to form a composite tubular member on the innersurface of the tubular mandrel; (iii) inserting an inner expandablemandrel within the composite tubular member; (iv) expanding the innerexpandable mandrel so as to cause the inner expandable mandrel to pressthe composite tubular member against the inner surface of the tubularmandrel; (v) curing the composite tubular member while being sandwichedbetween the inner expandable mandrel and the tubular mandrel; (vi)removing the inner expandable mandrel; (vii) placing a frame within thecomposite tubular member; and (viii) removing the tubular mandrel so asto obtain the composite tubular member with the frame placed therein.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the figures and the followingdetailed description.

BRIEF DESCRIPTION OF THE FIGURES

The novel features believed characteristic of the illustrativeembodiments are set forth in the appended claims. The illustrativeembodiments, however, as well as a preferred mode of use, furtherobjectives and descriptions thereof, will best be understood byreference to the following detailed description of an illustrativeembodiment of the present disclosure when read in conjunction with theaccompanying Figures.

FIG. 1 illustrates an apparatus for fabricating a tubular member of atubular structure in a vertical orientation, in accordance with anexample implementation.

FIG. 2 illustrates a top view of a tubular mandrel, in accordance withan example implementation.

FIG. 3 illustrates diagonal orientation of deposited composite material,in accordance with an example implementation.

FIG. 4 illustrates an inner mandrel, in accordance with an exampleimplementation.

FIG. 5 illustrates curing a tubular member, in accordance with anexample implementation.

FIG. 6 illustrates a single spiral of a geodesic frame, in accordancewith an example implementation.

FIG. 7 illustrates a geodesic frame, in accordance with an exampleimplementation.

FIG. 8 illustrates a zoomed-in view of the geodesic frame shown in FIG.7, in accordance with an example implementation.

FIG. 9 illustrates a geodesic frame with aircraft windows, in accordancewith an example implementation.

FIG. 10 illustrates removal of an inner mandrel, in accordance with anexample implementation.

FIG. 11 illustrates a geodesic frame prior to insertion into a tubularmember, in accordance with an example implementation.

FIG. 12 illustrates insertion of a geodesic frame into a tubular member,in accordance with an example implementation.

FIG. 13 illustrates a geodesic frame contacting a tubular member, inaccordance with an example implementation.

FIG. 14 extraction of a tubular structure, in accordance with an exampleimplementation.

FIG. 15 illustrates fastening spirals of a geodesic frame to each otherand fastening the geodesic frame to a tubular member, in accordance withan example implementation.

FIG. 16 is a flowchart of a method for manufacturing a tubularstructure, in accordance with an example implementation.

FIG. 17 is a flowchart of an example method for use with the method ofFIG. 16, in accordance with an example implementation.

FIG. 18 is a flowchart of an example method for use with the method ofFIG. 16, in accordance with an example implementation.

FIG. 19 is a flowchart of an example method for use with the method ofFIG. 16, in accordance with an example implementation.

FIG. 20 is a flowchart of an example method for use with the method ofFIG. 16, in accordance with an example implementation.

FIG. 21 is a flowchart of an example method for use with the method ofFIG. 16, in accordance with an example implementation.

DETAILED DESCRIPTION

The following detailed description describes various features andfunctions of the disclosed systems and methods with reference to theaccompanying figures. The illustrative system and method embodimentsdescribed herein are not meant to be limiting. It may be readilyunderstood that certain aspects of the disclosed systems and methods canbe arranged and combined in a wide variety of different configurations,all of which are contemplated herein.

Further, unless context suggests otherwise, the features illustrated ineach of the figures may be used in combination with one another. Thus,the figures should be generally viewed as component aspects of one ormore overall implementations, with the understanding that not allillustrated features are necessary for each implementation.

Additionally, any enumeration of elements, blocks, or steps in thisspecification or the claims is for purposes of clarity. Thus, suchenumeration should not be interpreted to require or imply that theseelements, blocks, or steps adhere to a particular arrangement or arecarried out in a particular order.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to skill in theart, may occur in amounts that do not preclude the effect thecharacteristic was intended to provide.

I. OVERVIEW

In examples, a composite tubular structure may include a tubular memberand a frame disposed within the tubular member to provide support forthe tubular member. For instance, a fuselage of an aircraft may be madeas a composite tubular structure that includes a skin and an internalframe to support the skin.

In an example, a method of fabricating the fuselage skin includesplacing the fuselage horizontally. Further, prior to inserting the framewithin the skin to support it, the fuselage is incomplete andunsupported and the skin supports its own weight against gravity.However, prior to inserting the frame within the frame, the skin mightnot possess enough internal strength to support its weight. Sagging,slumping, or changing the shape of the skin may thus occur as a resultof the horizontal positioning and the lack of internal structuralsupport for the skin. To alleviate this problem, additional bracing,jigs, and fixtures may be used to retain the shape of the skin.

Further, in this example, the frame of the fuselage is not fabricateduntil the skin “tube” is completed. In other words, the frame isfabricated in series with the skin, i.e., after the skin is fabricated.This may increase manufacturing time of the fuselage or any othertubular structure.

Disclosed herein are methods, processes, and structures that allows forthe frame to be fabricated in parallel with the skin to reduce overallmanufacturing time. Additionally, the disclosed methods and processesallow for the tubular member, e.g., the skin of the fuselage, to gainits structural integrity early in the fabrication process to reduce theuse of bracing, jigs, and fixtures. Additionally, rather than using acomplex series of frames and stringers to support the tubular member,disclosed herein is a geodesic frame that includes two oppositely-woundspirals that reduce the number of parts and cost of the frame.

II. EXAMPLE PROCESS FOR MANUFACTURING A TUBULAR STRUCTURE

As mentioned above, in fabricating tubular or barrel-shaped structures,gravity may change a shape of the structure or cause the structure to“slump.” To preclude this slumping from happening, jigs, clamps,fixtures, shims, etc. may be employed, thus adding cost, complexity, andtime to the manufacturing process. Alternatively, instead of orientingthe tubular structure horizontally, the structure may be orientatedvertically such that effect of gravity is reduced.

FIG. 1 illustrates an apparatus 100 for fabricating a tubular member ofa tubular structure in a vertical orientation, in accordance with anexample implementation. The apparatus 100 includes a vertical cylinder102 configured to rotate about its own longitudinal axis. For instance amotor or engine may be coupled to the vertical cylinder 102 andconfigured to rotate it about its own longitudinal axis. The verticalcylinder 102 surrounds a vertically-oriented tubular mandrel 104. Thetubular mandrel 104 is coupled to the vertical cylinder 102 and is thusconfigured to rotate therewith.

The tubular mandrel 104 may be segmented into arc segments. FIG. 2illustrates a top view of the tubular mandrel 104, in accordance with anexample implementation. As shown, the tubular mandrel 104 may includefour arc segments 104A, 104B, 104C, and 104D of a tube. Each of thesesegments may operate as a forming plate. The segments 104A-D areinterlocked to prevent formation of seams when a composite material isdeposited on an inner surface of the tubular mandrel 104 as describedbelow. Although FIG. 2 illustrates four segments. Any other number ofsegments could be used. For instance, two semi-circular halves could beused instead of the four arc segments 104A-D.

Further, the tubular mandrel 104 could also be segmented verticallybased on a length of the tubular member being manufactured. Forinstance, if the tubular member is a fuselage section of an aircraft,the length of the fuselage section may determine how many verticalsegments of the tubular mandrel 104 may be used. As shown in FIG. 1 asan example, instead of a single segment 104D, another vertical arcsegment 104DD is used. The vertical segments 104D and 104DD are alsointerlocked. The other segments 104A-C could also have correspondingvertical arc segments.

In some examples described herein, a tubular member being manufacturedis to be made of a composite material such as carbon fiber reinforcedpolymer (CFRP). The CFRP may, for example, include carbon fiberedembedded with an epoxy material. However, other example materials couldbe used as well. Referring back to FIG. 1, a CFRP wrapping device (e.g.,a robotic gantry device) 106 may be configured to reach into inner spaceof the tubular mandrel 104 and deposit CFRP material 108 on the innersurface of the tubular mandrel 104. In an example, the CFRP material 108may take the form of a tape that is deposited on the inner surface ofthe tubular mandrel 104.

The device 106 is configured to move vertically up and down within theinner space of the tubular mandrel 104 while depositing the CFRPmaterial 108 on the inner surface of the tubular mandrel 104. At thesame time, the tubular mandrel 104 is rotating along with the verticalcylinder 102. The combination of rotation of the tubular mandrel 104 andvertical motion of the device 106 causes the device 106 to deposit theCFRP material 108 in a diagonal pattern. By varying vertical speed ofthe device 106 and rotational speed of the tubular mandrel 104, adesired diagonal orientation of the fiber can be achieved.

FIG. 3 illustrates diagonal orientation of deposited composite material,in accordance with an example implementation. As illustrated, the x-axisin a graph 110 represents rotation of the tubular mandrel 104, while they-axis represents vertical motion of the device 106. Diagonal line 112represents diagonal orientation of the CFRP material 108 beingdeposited. This diagonal orientation is also the diagonal orientation ofthe fiber embedded within the polymer of the CFRP material 108.

The carbon fiber embedded in the CFRP material 108 gives strengththereto. Particularly, the CFRP material 108 has higher strength alongthe direction of the carbon fiber embedded therein. Thus, by controllingdiagonal orientation of the fiber by controlling the vertical motion ofthe device 106 and the rotational speed of the tubular mandrel 104, thefiber can be laid in the direction in which the strength of the CFRPmaterial 108 is most desired.

Further, the device 106 may be moved vertically up and down to achievemultiple passes and increase a thickness of the resulting tubular memberat given sections. For instance, if the tubular member is a section of afuselage, it may be desired to increase strength around doors andwindows of the aircraft. Thus, multiple passes may be performed by thedevice 106 for an area around a location of an aircraft door or window.

Further, the vertical speed of the device 106 may be changed based onwhich section of the tubular member is being formed. For instance, thedevice 106 may be slowed down to deposit more CFRP material 108 at aparticular area of the tubular member and may be configured to performmultiple passes along that particular area to increase its strength.

In examples, other constraints may be placed on rotational speed of thetubular mandrel 104 so as to maintain integrity of the CFRP material 108deposited on the inner surface of the tubular mandrel 104. Therotational speed determines a magnitude of a centripetal force that actsto maintain the CFRP material 108 attached to the inner surface of thetubular mandrel 104. If the centripetal force overcomes the effect ofgravity of the CFRP material 108, the CFRP material 108 would maintainits integrity and attachment to the tubular mandrel 104.

In addition to rotational speed of the tubular mandrel 104, otherfactors that affect the integrity of the CFRP material 108 includesdiameter of the tubular member being fabricated (i.e., the diameter ofthe inner surface of the tubular mandrel 104), weight of the CFRPmaterial 108 (e.g., weight per linear inch), stickiness and adhesivenessof a previously-applied layer of the CFRP material 108. These factors inthe aggregate may determine a net force that acts to hold the CFRPmaterial 108 in place while the tubular mandrel 104 is spinning. If thisnet force is greater than the gravitational force tending to cause theCFRP material 108 to “droop,” the CFRP material 108 may maintain itsintegrity and attachment to the inner surface of the tubular mandrel104.

In an example, the device 106 may be allowed to “overrun” the ends ofthe tubular mandrel 104. In this manner, the resulting tubular membermade of the CFRP material 108 may have “clean” ends, and “clean” entryand exit fiber placement.

During deposition of the CFRP material 108, rotation of the tubularmandrel 104 continues to maintain pressure on the CFRP material 108against the inner surface of the tubular mandrel 104 due to thecentripetal force resulting from the rotation. Otherwise, if therotation is stopped, the CFRP material 108 may droop and lose itsattachment to the tubular mandrel 104, because the CFRP material 108 isstill uncured at this stage of the process. In order to extract theuncured tubular member formed by the CFRP material 108, an inner mandrelmay be inserted within the tubular member made of the CFRP material 108while the tubular mandrel 104 and the CFRP material 108 attached theretoare still rotating.

FIG. 4 illustrates an inner mandrel 200, in accordance with an exampleimplementation. In examples, the inner mandrel 200 may be an expandablemandrel. For instance, the inner mandrel 200 may include an inflatablebladder. Once the inner mandrel 200 is fully inserted within a tubularmember 202 made of the CFRP material 108 shown in FIG. 1, the bladdermay be inflated, e.g., by a gas or other fluid. The bladder is inflateduntil it reaches the inner surface of the tubular member 202 and appliesa sufficient pressure to hold the CFRP material 108 of the tubularmember 202 against the tubular mandrel 104.

The inner mandrel 200 may be rotated prior to reaching the inner surfaceof the tubular member 202. For instance, once fully inserted within thetubular member 202, the inner mandrel 200 may be rotated prior toexpansion. Or, in another example, the inner mandrel 200 may be expandedand then prior to reaching the internal walls of the tubular member 202,the inner mandrel 200 may be rotated.

In examples, rotational speed of the inner mandrel 200 may besynchronized with the rotational speed of the tubular mandrel 104 andthe tubular member 202 attached thereto. Thus, if the tubular mandrel104 is rotating at a particular rotational speed, the inner mandrel 200is also rotated to substantially the same rotational speed of thetubular mandrel 104, e.g., within a threshold rotations per minute, RPM,such as 5 RPM. In this manner, if the rotational speeds aresynchronized, there is no relative speed between the inner mandrel 200and the tubular member 202 attached to and rotating with the tubularmandrel 104. As such, when the inner mandrel 200 is expanded and reachesthe inner wall of the tubular member 202, the inner mandrel 200 wouldnot scratch or drag against the inner wall of the tubular member 202.

Once the inner mandrel 200 applies sufficient pressure on the tubularmember 202, rotation of both the tubular mandrel 104 and the innermandrel 200 and the tubular member 202 sandwiched therebetween may bestopped. Rotation is stopped by, for example, stopping rotation of thevertical cylinder 102 and stopping rotation of any component (e.g., ashaft) that causes the inner mandrel 200 to rotate.

Up to his point of the process, the tubular member 202 has been orientedvertically such that effect of gravity on its shape is reduced and nosagging might occur. The next step in the process might be curing thetubular member 202. In some examples, curing may be performed while thetubular member 202 is vertically-oriented. In other examples,orientation of the tubular member 202 may be changed prior to curing.Particularly, now that the tubular member 202 is sandwiched between thetubular mandrel 104 and the inner mandrel 200, integrity of the tubularmember 202 is maintained, and its orientation could be changed to ahorizontal orientation to facilitate curing.

FIG. 5 illustrates curing the tubular member 202, in accordance with anexample implementation. In an example, the assembly including thetubular mandrel 104, the tubular member 202, and the inner mandrel 200is removed from the vertical cylinder 102 and rotated to a horizontalposition by a positioning device. The assembly may then be placed intoan autoclave 300, as shown in FIG. 5, to be cured at a particulartemperature for a predetermined amount of time. In another example, thevertical cylinder 102 along with the assembly may be inserted into theautoclave 300. In other words, the assembly including the tubularmandrel 104, the tubular member 202, and the inner mandrel 200 might notbe removed from the vertical cylinder 102 prior to rotating the assemblyto the horizontal position. Rather, the vertical cylinder 102 and theassembly are rotated to the horizontal position and inserted into theautoclave 300.

Other curing methods could be implemented. For instance, anout-of-autoclave curing process could be used. An example of suchprocess is ambient curing. Other curing methods are possible as well.

After the curing process is completed, the assembly including thetubular mandrel 104, the tubular member 202, and the inner mandrel 200is removed from the autoclave 300 and its temperature is allowed tostabilize. Next, the inflatable inner mandrel 200 is de-pressurized andremoved. After removing the inner mandrel 200, the tubular member 202could receive a frame therein.

If the frame is fabricated and assembled after the tubular member 202 isfabricated, manufacturing of the tubular structure is inefficient.However, if the frame can be fabricated independent from, and inparallel with, tubular member 202, manufacturing time and cost could bereduced. This parallel fabrication can be achieved by a geodesic frame.The geodesic frame may be composed of at least two oppositely-woundcoils or spirals combined and fastened to make a strong, lightweightinner structure for the tubular member 202. In an example, if thetubular member 202 is a fuselage, the spirals could be made of titaniumto achieve the desired strength and light weight.

FIG. 6 illustrates a single spiral 400 of a geodesic frame, inaccordance with an example implementation. A length “L” of the spiralmay be the length of the tubular member 202 and a diameter “D” of thespiral may be the inside diameter of the tubular member 202. Anotherspiral could be oppositely wound and coupled to the spiral 400. Forinstance, if the spiral 400 is wound in a clockwise direction, anotherspiral could be wound counter-clockwise and coupled to the spiral 400 toform a cage-like geodesic frame.

FIG. 7 illustrates a geodesic frame 402, in accordance with an exampleimplementation. The geodesic frame 402 includes the spiral 400 andanother spiral oppositely wound with respect to the spiral 400. FIG. 8illustrates a zoomed-in view of the geodesic frame 402, in accordancewith an example implementation. As shown, the geodesic frame 402includes a second spiral 404 oppositely wound with respect to the spiral400. In examples, the geodesic frame 402 may include a greater number ofspirals.

The portion shown in FIG. 8 is toward an end of the geodesic frame 402and includes an end plate 406. The end plate 406 facilitates handlingthe geodesic frame 402 and may remain coupled to the spirals 400 and 404after insertion into the tubular member 202 or may be removed.

The two oppositely-wound spirals 400 and 404 cross each other atmultiple crossing or intersection points such as intersection point 408.In an example, the spirals 400 and 404 may be coupled to each other atthe intersection points via fasteners or any kind of adhesive bonding.In another example, a separate coupling fitting could be attached atsome or all of the intersection points to fasten the spiral 400 and 404together. In still another example, one or both spirals 400 and 404 mayhave notches (e.g., V-shaped notches) that an opposite spiral may passthrough. A tight fit may be created at the notches to couple the spirals400 and 404 to each other. Additionally or alternatively, fasteners oradhesive could be used at the notch locations to couple the spirals 400and 404 to each other.

In an example, the spirals 400 and 404 may have a cross section with a“U-shaped,” “C-shaped,” “L-shaped,” “T-shaped,” or “I-shaped” channel.For instance, the two spirals 400 and 404 may have two opposing“U-shaped” cross sections, and one spiral may fit within the otherspiral at the crossing points. Alternatively, one spiral may passunderneath the other spiral and a fastener may be used to couple the twospirals as described below with respect to FIG. 15.

The arrangement of the spiral 400 and 404 of the geodesic frame 402 maycreate strong crossing joints and good structural rigidity can beattained. By varying the pitch and the number of coils of a spiral, theangularity or orientation of these joins can be varied.

In an example where the tubular element 202 and the geodesic frame 402pertain to a fuselage, orientation of the spirals 400 and 400 can bedetermined such that window placement is facilitated. FIG. 9 illustratesthe geodesic frame 402 with aircraft windows, in accordance with anexample implementation. As mentioned, the pitch and number of coils ofthe spirals 400 and 404 may be adjusted to create a space for windowssuch as window 410 of an aircraft.

Installation or insertion of the geodesic frame 402 into the tubularmember 202 is described next.

FIG. 10 illustrates removal of the inner mandrel 200, in accordance withan example implementation. As mentioned above, after the curing processis completed, the assembly including the tubular mandrel 104, thetubular member 202, and the inner mandrel 200 is removed from theautoclave 300 and its temperature is allowed to stabilize. Next, theinflatable inner mandrel 200 is de-pressurized and removed. The innermandrel 200 can, for example, be pulled from the inner space of thetubular member 202 by way of a robotic arm or manipulator. The tubularmandrel 104 may be retained so as to maintain a circular or cylindricalshape of the tubular member 202. Meanwhile, the geodesic frame 402 mayhave been fabricated or assembled independently in parallel withfabrication of the tubular member 202.

FIG. 11 illustrates the geodesic frame 402 prior to insertion into thetubular member 202, and FIG. 12 illustrates insertion of the geodesicframe 402 into the tubular member 202, in accordance with an exampleimplementation. As shown in FIG. 11, the geodesic frame 402 may have adiameter “d₁” and the tubular member 202 may have an inside diameter“d₂.” These diameters may be substantially the same or the diameter “d₁”may be slightly larger than the diameter “d₂.” In order to facilitateinsertion of the geodesic frame 402 into the tubular member 202, thediameter “d₁” may be slightly decreased temporarily until the geodesicframe 402 is inserted.

As shown in FIG. 12, the geodesic frame 402 may be coupled to horizontalassembly mandrel 500, which could be a manipulator or an arm of arobotic device 502, for example. The robotic device 502 may beconfigured to slightly, axially stretch the geodesic frame 402 via themandrel 500 so as to decrease the outside diameter “d₁” to a diameter“d₃,” which is smaller than both “d₁” and “d₂.” The mandrel 500 may thenplace the geodesic frame 402 into the tubular member 202.

FIG. 13 illustrates the geodesic frame 402 contacting the tubular member202, in accordance with an example implementation. As shown in FIG. 13,the mandrel 500 may be slowly retracted, allowing the geodesic frame 402to expand back to its un-stretched diameter “d₁.” As a result of theexpansion, the geodesic frame 402 contacts the inner surface of thetubular member 202, and thus supports the tubular member 202. In anotherexample, the expansion of the geodesic frame 402 could also beaccomplished by compressing it by the mandrel 500 to increase the outerdiameter of the geodesic frame 402 and bring the geodesic frame 402 intocontact with an inner surface of the tubular member 202.

In examples, the geodesic frame 402 may be pre-fastened to the tubularmember 202 prior to extraction of the tubular member 202 and thegeodesic frame 402 from the tubular mandrel 104. For example, fastenerscould be drilled from the inside out to pre-fasten the geodesic frame402 to the tubular member 202. In this example, the tubular mandrel 104may include replaceable inserts at the locations where the fasteners aredrilled to prevent the fasteners from breaking out through the tubularmandrel 104. These fasteners could later be replaced by countersunk“outside-in” fasteners.

In the examples where the tubular member 202 and the geodesic frame 402represent a fuselage, windows and doors of the aircraft could be cut outand fitted at this stage of the manufacturing process. Edges of thetubular member 202 could then be trimmed and finished.

The tubular member 202 and the geodesic frame 402 disposed therein couldthen be extracted from the tubular mandrel 104. FIG. 14 illustratesextraction of a tubular structure, in accordance with an exampleimplementation. FIG. 14 shows the tubular member 202 disposed within thetubular mandrel 104. The geodesic frame 402 is not shown to reducevisual clutter in the drawing. As mentioned above, the tubular mandrel104 may include several interlocked arc segments such as the segments104A-D. These segments could be disassembled from around the tubularmember 202 as illustrated by removing the segments 104A in FIG. 14. Thetubular member 202 and the geodesic frame 402 disposed therein couldthen be extracted.

Permanent fasteners can be installed to couple the spirals 400 and 404of the geodesic frame 402 to each other and couple the geodesic frame402 to the tubular member 202. FIG. 15 illustrates fastening the spirals400 and 404 of the geodesic frame 402 to each other and fastening thegeodesic frame 402 to the tubular member 202, in accordance with anexample implementation. As shown, a fastener 700 could be used to joinan outside spiral, i.e., the spiral 400 in FIG. 15, of the geodesicframe 402 to the tubular member 202, which is made of compositematerial.

Similarly, another fastener 702 joins or couples the spirals 400 and 404to each other. In the example of manufacturing a fuselage, the spirals400 and 404 could be made of titanium (Ti). In this example, thefastener 702 is a Ti—Ti joint fastener. In FIG. 15, the spirals 400 and404 are illustrated having “C,” or “U” channel-shaped cross sections.Other cross sections could be used and the example shown is forillustration only.

The spirals 400 and 404 overlap each other in FIG. 15. However, otherconfigurations are possible. For instance, the two opposing “C” or “U”channel-shaped cross sections may fit with each other instead ofoverlapping. Additional reinforcements could be added at the crossjoints between the spirals 400 and 404 to increase integrity of thegeodesic frame 402 and the resulting composite tubular structure thatincludes the tubular member 202 and the geodesic frame 402.

A secondary structure could be coupled to the geodesic frame 402. Thesecondary structure could, for example, contact a free inside surface704 of the spiral 404.

Although the process described above illustrates using a geodesic frameincluding two oppositely-would spirals, other frame types could be usedto support the tubular member 202.

Beneficially, the process described above allows for fabricating thegeodesic frame 402 in parallel with the fabricating the tubular member202 to reduce overall manufacturing time. Additionally, the processallows for the tubular member 202 to be vertically-oriented until itgains its structural integrity to reduce the use of bracing, jigs, andfixtures. Additionally, rather than using a complex series of frames andstringers to support the tubular member 202, the geodesic frame 402described above reduces the number of parts and cost of the framesupporting the tubular member 202.

III. EXAMPLE METHODS

FIG. 16 is a flowchart of a method 800 for manufacturing a tubularstructure, in accordance with an example implementation. The method 800represents a process that may be used, for example, to make or preparethe tubular structure including the tubular member 202 and the geodesicframe 402 as described above with respect to FIGS. 1-15. The method 800may include one or more operations or actions as illustrated by one ormore of blocks 802-818. Although the blocks are illustrated in asequential order, these blocks may in some instances be performed inparallel, and/or in a different order than those described herein. Also,the various blocks may be combined into fewer blocks, divided intoadditional blocks, and/or removed based upon the desired implementation.

At block 802, the method 800 includes rotating a tubular mandrel about alongitudinal axis of the tubular mandrel, where the tubular mandrel isvertically-oriented. As described with respect to FIG. 1, a verticalcylinder (e.g., the vertical cylinder 102) may be configured to rotateabout its own longitudinal axis. The vertical cylinder may surround avertically-oriented tubular mandrel (e.g., the tubular mandrel 104). Thetubular mandrel may include a plurality of interlocked arc segments of atube (e.g., the segments 104A-D and 104DD). The tubular mandrel iscoupled to the vertical cylinder and is thus configured to rotatetherewith.

At block 804, the method 800 includes depositing a composite material onan inner surface of the tubular mandrel as the tubular mandrel isrotated so as to form a composite tubular member on the inner surface ofthe tubular mandrel. A CFRP wrapping device (e.g., a robotic gantrydevice such as the device 106) may be configured to reach into the innerspace formed within the tubular mandrel and deposit CFRP material (e.g.,the CFRP material 108) on an inner surface of the tubular mandrel.

FIG. 17 is a flowchart of a method for use with the method 800, inaccordance with an example implementation. At block 805, the methodincludes depositing the composite material using a CFRP wrapping devicethat is moving vertically within the tubular mandrel as the tubularmandrel is rotated. The combination of rotation of the tubular mandreland vertical motion of the CFRP wrapping device causes the CFRP wrappingdevice to deposit the CFRP material in a diagonal pattern. By varyingvertical speed of the device and rotational speed of the tubularmandrel, a desired diagonal orientation of the fiber can be achieved.

Referring back to FIG. 16, at block 806, the method 800 includesinserting an inner expandable mandrel within the composite tubularmember. As described with respect to FIG. 4, an inner mandrel (e.g., theinner mandrel 200) may be an expandable mandrel. For instance, the innermandrel may include an inflatable outer bladder. The inner expandablemandrel may be inserted within the tubular member in a deflated state tofacilitate the insertion.

At block 808, the method 800 includes expanding the inner expandablemandrel so as to cause the inner expandable mandrel to press thecomposite tubular member against the inner surface of the tubularmandrel. Once the inner mandrel is fully inserted within a tubularmember made of the CFRP material, the method 800 includes expanding theinner expandable mandrel.

FIG. 18 is a flowchart of a method for use with the method 800, inaccordance with an example implementation. In the example where theinner mandrel includes a bladder, at block 809, the method includesinflating the bladder until an outer surface of the bladder reaches theinner surface of the tubular member and applies a sufficientpredetermined pressure (e.g., 100 pounds per square inch (psi), orwithin a range of about 50-250 psi in other examples) to hold or securethe CFRP material of the tubular member against the inner surface of thetubular mandrel.

The inner mandrel may be rotated prior to reaching the inner surface ofthe tubular member. For instance, once fully inserted within the tubularmember, the inner mandrel may be rotated prior to expansion. Or, inanother example, the inner mandrel may be expanded and then prior toreaching the internal walls of the tubular member, the inner mandrel maybe rotated.

In examples, rotational speed of the inner mandrel may be synchronizedwith the rotational speed of the tubular mandrel and the tubular memberattached thereto. In other words, if the tubular mandrel is rotating ata particular rotational speed, the inner mandrel is also rotated tosubstantially the same rotational speed of the tubular mandrel.

FIG. 19 is a flowchart of an example method for use with the method 800,in accordance with an example implementation. Once the inner mandrelapplies sufficient pressure on the tubular member, at block 810, themethod includes stopping rotation of the tubular mandrel, the innermandrel, and the tubular member sandwiched therebetween.

Referring back to FIG. 16, at block 811, the method 800 includes curingthe composite tubular member while being sandwiched between the innerexpandable mandrel and the tubular mandrel. In an example, the assemblyincluding the tubular mandrel, the tubular member, and the inner mandrelis removed from the vertical cylinder.

FIG. 20 is a flowchart of an example method for use with the method 800,in accordance with an example implementation. At block 812, the methodincludes orientating the tubular mandrel, the tubular member, and theinner expandable mandrel in a horizontal position, prior to the curing,by a positioning device as described with respect to FIG. 5. Theassembly may then be placed into an autoclave to be cured at aparticular temperature for a predetermined amount of time (e.g., anhour). In another example, the vertical cylinder along with the assemblyis inserted into the autoclave.

Other curing methods could be implemented. For instance, anout-of-autoclave curing process could be used. An example of suchprocess is ambient curing. Other curing methods are possible as well.

Referring back to FIG. 16, at block 813, the method 800 includesremoving the inner expandable mandrel. After the curing process iscompleted, the assembly including the tubular mandrel, the tubularmember, and the inner mandrel is removed from the autoclave and itstemperature is allowed to stabilize. Next, the inflatable inner mandrelmay de-pressurized or deflated and removed. After removing the innermandrel, the tubular member could receive a frame therein.

At block 814, the method 800 includes placing a frame within thecomposite tubular member. The frame can be fabricated independent fromand in parallel with tubular member so as to reduce manufacturing timeand cost. Any type of supporting frame could be used. As an example, theframe could be a geodesic frame such as the geodesic frame 402 describedabove. The geodesic frame may be composed of at least twooppositely-wound spirals combined and joined at intersection points ofthe two oppositely-wound spirals to make a strong, lightweight innersupporting structure for the tubular member.

FIG. 21 is a flowchart of an example method for use with the method 800,in accordance with an example implementation. In order to facilitateinsertion of the geodesic frame, or any other frame, into the tubularmember, at block 815, the method includes axially stretching thegeodesic frame to reduce a diameter of the geodesic frame. At block 816,the method 800 then includes inserting the axially stretched geodesicframe within the composite tubular member. At block 817, the methodfurther includes releasing the geodesic frame to cause the diameter ofthe geodesic frame to expand, thereby causing the geodesic frame tocontact and support the composite tubular member.

Referring back to FIG. 16, at block 818, the method 800 includesremoving the tubular mandrel so as to obtain the composite tubularmember with the frame placed therein. The tubular member and the framedisposed therein could be extracted from the tubular mandrel by, forexample, disassembling arc segments of the tubular mandrel as describedwith respect to FIG. 14. The tubular member and the frame disposedtherein could then be extracted. In this manner, a composite tubularstructure that includes the tubular member and the frame disposedtherein is obtained.

IV. CONCLUSION

It should be understood that arrangements described herein are forpurposes of example only. As such, those skilled in the art willappreciate that other arrangements and other elements (e.g., machines,interfaces, orders, and groupings of operations, etc.) can be usedinstead, and some elements may be omitted altogether according to thedesired results.

While various aspects and implementations have been disclosed herein,other aspects and implementations will be apparent to those skilled inthe art. The various aspects and implementations disclosed herein arefor purposes of illustration and are not intended to be limiting, withthe true scope being indicated by the following claims, along with thefull scope of equivalents to which such claims are entitled. It is alsoto be understood that the terminology used herein is for the purpose ofdescribing particular implementations only, and is not intended to belimiting.

What is claimed is:
 1. A method comprising: rotating a tubular mandrelabout a longitudinal axis of the tubular mandrel, wherein the tubularmandrel is vertically-oriented; depositing a composite material on aninner surface of the tubular mandrel as the tubular mandrel is rotatedso as to form a composite tubular member on the inner surface of thetubular mandrel; inserting an inner expandable mandrel within thecomposite tubular member; expanding the inner expandable mandrel so asto cause the inner expandable mandrel to press the composite tubularmember against the inner surface of the tubular mandrel; curing thecomposite tubular member while being sandwiched between the innerexpandable mandrel and the tubular mandrel; removing the innerexpandable mandrel; placing a frame within the composite tubular member;and removing the tubular mandrel so as to obtain the composite tubularmember with the frame placed therein.
 2. The method of claim 1, whereinthe tubular mandrel is rotated at a particular rotational speed, andwherein the inner expandable mandrel is rotated at the particularrotational speed such that respective rotations of the inner expandablemandrel and the tubular mandrel are synchronized.
 3. The method of claim1, further comprising: stopping rotation of the tubular mandrel prior tothe curing.
 4. The method of claim 3, wherein the inner expandablemandrel includes an inflatable bladder, and wherein expanding the innerexpandable mandrel comprises: inflating the inflatable bladder until anouter surface of the inflatable bladder applies a predetermined pressureon the composite tubular member to secure the composite tubular memberagainst the inner surface of the tubular mandrel upon stopping therotation of the tubular mandrel.
 5. The method of claim 1, furthercomprising: orientating the tubular mandrel, the composite tubularmember, and the inner expandable mandrel in a horizontal position priorto the curing.
 6. The method of claim 1, wherein the tubular mandrelcomprises a plurality of interlocked arc segments of a tube.
 7. Themethod of claim 1, wherein depositing the composite material on theinner surface of the tubular mandrel comprises: depositing the compositematerial using a device that is moving vertically within the tubularmandrel as the tubular mandrel is rotated.
 8. The method of claim 1,wherein the frame is a geodesic frame comprising two oppositely-woundspirals joined at intersection points of the two oppositely-woundspirals.
 9. The method of claim 8, wherein placing the geodesic framewithin the composite tubular member comprises: axially stretching thegeodesic frame to reduce a diameter of the geodesic frame; inserting theaxially stretched geodesic frame within the composite tubular member;and releasing the geodesic frame to cause the diameter of the geodesicframe to expand, thereby causing the geodesic frame to contact thecomposite tubular member.
 10. The method of claim 8, wherein at leastone of the two oppositely-wound spirals of the geodesic frame has aU-shaped or an L-shaped cross section.
 11. A method for manufacturing atubular structure, the method comprising: rotating a tubular mandrelabout a longitudinal axis of the tubular mandrel; depositing a compositematerial on an inner surface of the tubular mandrel as the tubularmandrel is rotated so as to form a composite tubular member on the innersurface of the tubular mandrel; inserting an inner expandable mandrelwithin the composite tubular member; expanding the inner expandablemandrel so as to cause the inner expandable mandrel to press thecomposite tubular member against the inner surface of the tubularmandrel; removing the inner expandable mandrel; inserting a geodesicframe within the composite tubular member; and removing the tubularmandrel so as to obtain the composite tubular member with the geodesicframe placed therein.
 12. The method of claim 11, wherein rotating thetubular mandrel about the longitudinal axis thereof comprises rotatingthe tubular mandrel while the tubular mandrel is vertically-oriented.13. The method of claim 11, further comprising: prior to removing theinner expandable mandrel, curing the composite tubular member whilebeing sandwiched between the inner expandable mandrel and the tubularmandrel.
 14. The method of claim 13, further comprising: orientating thetubular mandrel, the composite tubular member, and the inner expandablemandrel in a horizontal position prior to the curing.
 15. The method ofclaim 11, wherein inserting the geodesic frame comprises inserting thegeodesic frame comprising two oppositely-wound spirals joined atintersection points of the two oppositely-wound spirals.
 16. The methodof claim 11, wherein inserting the geodesic frame within the compositetubular member comprises: axially stretching the geodesic frame toreduce a diameter of the geodesic frame; inserting the geodesic framewithin the composite tubular member while being axially stretched; andreleasing the geodesic frame to cause the geodesic frame to expand,thereby causing the geodesic frame to contact the composite tubularmember.
 17. The method of claim 11, wherein the composite tubular memberincludes one or more sections having an increased thickness compared toother sections of the composite tubular member, and wherein depositingthe composite material to form the composite tubular member on the innersurface of the tubular mandrel comprises: depositing the compositematerial via a longitudinally-moving device, wherein a longitudinalspeed of the longitudinally-moving device and number of passes of thelongitudinally-moving device at the one or more sections are varied toincrease thickness of the composite material at the one or more sectionsof the composite tubular member.
 18. The method of claim 11, wherein theinner expandable mandrel comprises an inflatable bladder, and whereinexpanding the inner expandable mandrel comprises: inflating theinflatable bladder until an outer surface of the inflatable bladderapplies a predetermined pressure on the composite tubular member tosecure the composite tubular member against the inner surface of thetubular mandrel.
 19. The method of claim 11, wherein the tubular mandrelcomprises a plurality of interlocked arc segments of a tube, and whereinremoving the tubular mandrel comprises: disassembling the plurality ofinterlocked arc segments from around the composite tubular member. 20.The method of claim 11, wherein rotating the tubular mandrel comprisesrotating the tubular mandrel at a particular rotational speed, andwherein the method further comprises: rotating the inner expandablemandrel at the particular rotational speed so as to synchronizerespective rotations of the inner expandable mandrel and the tubularmandrel.